This invention relates to the augmentor of a turbofan engine and particularly to fuel control means therefor.
Heretofore, the fuel admitted to the agumentor was controlled by utilizing an engine control parameter that sets up a value indicative of W.sub.f /P.sub.3 : Where W.sub.f is fuel flow in pounds/hour and P.sub.3 is compressor discharge air pressure in psia. This value in essence serves as a rough estimate of the fuel/air ratio in the aurgmentor, but in reality is not deemed a valid indication thereof. While such a control parameter for many purposes is practical and still is employed, it has its shortcomings inasmuch as it does not lend itself to account for some of the adverse conditions inherent in the augmentors.
I have found that I can improve augmentor effectiveness by controlling the fuel to the hot and cold sections of the augmentor by developing a signal for each of the fuel values in these sections indicative of the hot and cold fuel/air ratio. In one embodiment, it is contemplated that the air flow in the hot section (core air) and the airflow in the cold section, fan bypass air, is synthesized and the fuel/air ratio is calculated to control the segmented fuel nozzles in each of the sections. In another preferred embodiment, the core airflow is similarly synthesized and, however, the total engine airflow is synthesized. The two are subtracted and the difference is the cold airflow. Similarly, the fuel/air ratio is calculated to provide improved fuel control schedule to the augmentor. The fact that fuel air ratio is utilized as the control parameter affords a host of potential augmentor improvements. For example, the augmentor can now avoid rumble, poor ignition and durability limits. Transient variations in bypass ratio are compensated for and a constant f/A is maintained.